A new Pew report sheds light on the still-significant population of American adults – 15%, in fact – who don't use the Internet.

Among those who remain offline, the most common reason given is that they’re “just not interested,” as cited by 21%. The next most common reason, cited by 13%, is a pretty good one – “I don’t have a computer.”

Pew says the main reason Americans don’t use the Internet is “relevance,” which the research firm defined as the sentiment behind those who are disinterested, think it’s a waste of time, are too busy or just don’t need or want to use the Internet. This accounted for 34% of the survey’s respondents.

A close second, however, was “usability,” which included those who cited difficulty learning the Internet for a variety of reasons and those who were worried about virus, spam and hackers. At 32% of the respondents, Pew says “this figure is considerably higher than in earlier surveys.”

Price was the third-most cited reason. At 19%, it marked a drop from the 21% who claimed price kept them offline when the survey was conducted in 2010. However, just 11% cited price in 2007, as did 16% in 2009, suggesting that cost has become a more significant barrier to Internet adoption in the past four years.

Availability and access to the Internet was an obstacle for 7% of respondents, up slightly from 6% in 2010, but down substantially from the 18% who lacked access in 2009.

As usual, Pew provided demographics for its survey respondents, and they followed a trend that was made clear in earlier editions – older Americans, those with low income and/or poor education levels make up most of the offline population. Forty-four percent of respondents were 65 and older, and another 17% were aged 50 to 64. A combined 10% were aged 18 to 49, according to the report.

In terms of education, 41% had no high school diploma, compared to 22% of offline Americans who had just a high school diploma. Another 8% remained offline despite having completed “some college,” and 4% of respondents had earned at least one college degree.

The respondents largely belonged to lower-income levels, with 24% earning less than $30,000 per year and another 12% between $30,000 and $49,999. Just 4% of respondents earned more than $75,000 per year.

While 63% of respondents say they would need someone to help them if they wanted to go online, another 17% claim to know enough to use the Internet. Indeed, when Pew asked respondents if they would need assistance going online, 13% said they would not want to.

Another 55% of respondents backed up this claim, telling Pew that they have never asked a family member or friend to complete an online task or look something up on the Internet for them, although 44% said they have.

While the total number of American adults on the Internet is up from 78% as of Pew’s report in August 2011, the trends don’t appear to have changed for those in the demographics that have made up the offline population since Pew first began keeping track.

“Those who do not use the Internet often do not feel any need to try it, some are wary of the technology, and others are unhappy about what they hear about the online world,” a Pew report published in September 2000 concluded.

Colin Neagle covers emerging technologies and the startup scene for Network World. Follow him on Twitter and keep up with the Microsoft, Cisco and Open Source community blogs. Colin's email address is cneagle@nww.com.

Join the Network World communities on Facebook and LinkedIn to comment on topics that are top of mind.